Polycarbonate resins (hereinafter sometimes abbreviated as “PC”) are widely used in various industrial fields including automobile, OA appliance, and electric and electronic products. However, there is a strong demand for improvement of the flame retardancy for the resin materials used in the applications including OA appliance, and electric and electronic products, and numerous flame retardants have been developed to fulfill such demands. The flame retardants used for the polycarbonate resin have mostly been bromine compounds which were optionally used with antimony trioxide. Such resin composition, however, generates bromine gas in the burning of the resin, and this invites environmental contamination. In view of such situation, use of a phosphorus flame retardant, for example, a phosphate ester simultaneously with or without the bromine compound has been recently reported as an attempt to reduce the amount of the bromine compound used. However, such phosphorus flame retardants has a drawback that it decomposes during its use inviting loss of the mechanical strength of the resin composition, and such phosphorus flame retardants could not completely solve the problem of environmental contamination.
With regard to such non-phosphorus flame retardant materials or non-phosphorus, non-bromine flame retardant materials, Patent Document 1 (JP-A 51-045159), for example, proposes a flame retardant polycarbonate resin composition comprising an organic acid salt such as sulfonate salt of an alkaline metal or alkaline earth metal, polytetrafluoroethylene, and an aromatic polycarbonate; Patent Document 2 (JP-A 06-073281) proposes a flame retardant polycarbonate resin composition comprising a polycarbonate, an alkali metal salt or an alkaline earth metal salt of a perfluoroalkanesulfonic acid, and epoxy resin; and Patent Document 3 (JP-A 2004-155938) proposes a flame retardant polycarbonate resin composition comprising a polycarbonate resin, a metal salt of an aromatic sulfur compound, a fiber-forming fluorine-containing polymer, and a polyorganosiloxane. These flame retardant polycarbonate resin compositions, however, did not exhibit the excellent transparency characteristic to the polycarbonate resin, and also suffered from the drawbacks including loss of melt thermal stability when the flame retardant is added at an amount sufficient for realizing the intended flame retardancy, yellowing and silvering of the molded article, and drastic decrease in the mechanical strength.
Patent Document 4 (JP-A 2003-064229) proposes a flame retardant resin composition comprising a metal sulfonate salt of styrene polymer in which an aromatic monomer unit having sulfonate group in the aromatic skeleton constitutes 15 to 45% by mole of the total monomer units, a styrene polymer having a content of the metal sulfate of up to 5% by weight, and a polycarbonate. This flame retardant resin composition suffered from insufficient thermal stability that invited yellowing of the composition as well as insufficient weatherability.
In the case of the polycarbonate resin compositions having incorporated therein a halogen-free, phosphorus-free flame retardant as described above, the compositions suffered from the drawback that the composition was insufficient in the flame retardancy, and when a flame retardant was incorporated at an amount sufficient for realizing the flame retardancy, the composition exhibited loss of the melt thermal stability and the molded article underwent yellowing and drastic loss of mechanical strength.
In the meanwhile, a number of polymer alloys with another thermoplastic resin have been developed to further improve and modify various properties of the polycarbonate resin. One such polycarbonate composition is the one prepared by blending a polycarbonate resin with a styrene/acrylonitrile graft copolymer such as ABS resin, and this material is widely used in the field of automobiles as well electric and electronic appliances because it is a thermoplastic resin material having excellent mechanical properties, flowability, and thermal properties. In the field where the flame retardancy is required, a flame retardant is blended in such composition. Exemplary halogen-free flame retardant materials having reduced environmental stress include a resin composition comprising a polycarbonate resin and an ABS resin having a phosphorus flame retardant incorporated therein (see for example, Patent Documents 5 and 6: JP-A 02-115262 and JP-A 02-032154). These materials, however, suffered from the problems such as decrease in the distortion temperature under load as well as generation of the mold deposit.
Patent Document 7 (JP-A 11-172063) proposes a resin composition comprising a polycarbonate resin and an ABS resin having a metal sulfonate salt of the polystyrene incorporated therein. However, when the metal sulfonate salt was incorporated at an amount sufficient for realizing the flame retardancy, impact strength and distortion temperature under load of the resin composition decreased, and the molded article exhibited insufficient outer appearance. Patent Document 8 (JP-A 2002-167499) proposes a flame retardant resin composition formed form a polymer comprising a polycarbonate resin, a styrene resin, silicon, boron, and oxygen which has skeleton substantially constituted from silicon-oxygen bond and boron-oxygen bond, and which has aromatic ring in its molecule. This resin composition, however, was insufficient in the flame retardancy and impact strength. Patent Document 9 (JP-A 2004-035587) proposes a flame retardant resin composition comprising an aromatic polycarbonate resin, a styrene resin, an organic alkali metal salt and/or organic alkaline earth metal salt, and a silicone compound having functional groups. This flame retardant resin composition was commercially unpractical due to the insufficient glossiness and insufficient tensile elongation at the welded portion.
As described above, the resin compositions comprising a polycarbonate resin, a styrene resin such as ABS, and a flame retardant have been insufficient in distortion temperature under load, impact strength, and weld strength, and exhibited mold deposit and unfavorable outer appearance, and, currently available flame retardant resin compositions have been unacceptable for use in commercial applications.